Keeping stable

Delphi is developing a new Active Stabiliser Bar System (ASBS) that delivers better steering feel, improved vehicle dynamics, superior comfort and greater tuning capability compared with today's technologies.

The system is claimed to be the first to provide continuous across-centre control and is 60 per cent lighter and around 65 per cent more compact than the company's previous system.

Delphi was first to market with an Active Stabiliser Bar System in 1999 and has subsequently developed both linear and rotary systems for a range of applications.

In 2005, Delphi's second generation system was launched on the Range Rover Sport. The ball screw rotary actuator technology provides a high angular articulation and converts around 95 per cent of pump energy into hydraulic pressure.

A traditional stabiliser bar improves vehicle stability through corners by reducing roll angle and managing the tyre-to-road interface. High performance vehicles and heavy vehicles with a high centre of gravity typically require stiff, large diameter stabiliser bars but these can substantially reduce ride comfort and refinement and can also reduce traction in some conditions.

Traditional stabiliser bars also restrict wheel travel, decreasing off-road performance for SUVs, and can create an effect known as 'head toss' that can be particularly uncomfortable in vehicles where the occupants are seated high.

Delphi's ASBS technology splits the stabiliser bar in the middle, allowing a computer-controlled actuator to apply a variable level of torque to each end. When the vehicle is travelling in a straight line, the system effectively de-couples the stabiliser bars from the vehicle, improving ride comfort and allowing up to 88 degrees of free stabiliser bar rotation for greater wheel articulation. In a corner, anti-roll torque is instantly applied and can be optimised for any driving condition in just 20msec.

The company has also developed a new hydraulic control system for the ASBS. Contemporary systems use a directional control valve to reverse the hydraulic pressure and hence the force applied to the roll bars. This gives poor steering feel around centre, with limited control authority when travelling in a straight line and can also generate significant noise.

Delphi's patented continuous pressure control system solves these issues by eliminating the need to switch the direction in which pressure is applied and by maintaining a constant small on-centre pressure to improve steering feel and response.

Switching noise is eliminated and two channel control allows component sharing front-to-rear and the integration of different control calibrations for comfort and sport modes. Because it is truly active (i.e. it can apply force to the suspension), the system can also be used to tune roll damping. The efficiency of the system further reduces noise and allows a proven pump to be used with a small reservoir and easily routed hoses.

Other innovations throughout the system, including new techniques for attaching the roll bars to the actuators, reduce the size of the system.

Delphi expects to enter production with a linear actuator system in 2011 and with a rotary actuator system in 2012, both for European customers.